#include <cstdio>
#include <cmath>

int main() {
    double x1, y1, x2, y2;
    scanf("%lf%lf", &x1, &y1);
    scanf("%lf%lf", &x2, &y2);
    printf("%.4lf\n", sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)));

    return 0;
}
